1. Field of Invention
The present invention relates to a chip package having asymmetric molding, and particularly to a chip package having a lead frame.
2. Description of the Related Art
To a dynamic random access memory (DRAM), the packages can be categorized into small outline J-lead packages (SOJ packages) and thin small outline packages (TSOP), both of which have fast transmission rate, good heat dissipation and compact size. In terms of lead frames, no matter SOJ packages or TSOP can be further classified into lead on chip packages (LOC packages) disclosed by U.S. Pat. No. 4,862,245 and chip on lead packages disclosed by U.S. Pat. No. 4,989,068.
FIG. 1A is a schematic section view of a conventional TSOP having LOC configuration. Referring to FIG. 1A, a conventional TSOP 100a includes a lead frame 110, a chip 120, an adhesive layer 130, a plurality of first bonding wires 140a and a molding compound 150. Wherein, the lead frame 110 has inner lead portions 112 and outer lead portions 114. The chip 120 is fixed on the lower surfaces of the inner lead portions 112 through the adhesive layer 130 disposed between the chip 120 and the inner lead portions 112. The first bonding wires 140a are electrically connected between the chip 120 and the corresponding inner lead portions 112, respectively. The molding compound 150 is used for encapsulating the inner lead portions 112, the chip 120, the adhesive layer 130 and the first bonding wires 140a. 
It is noted that the thickness D1 of the molding compound 150 residing over the outer lead portions 114 is in the proportion of 1:3 to the thickness D2 of the molding compound 150 residing under the outer lead portions 114. Therefore, as the molding compound 150 condenses and shrinks, the TSOP 100a will be warped and damaged.
FIG. 1B is a schematic section view of another conventional TSOP having LOC configuration. Continue referring to FIG. 1B, it is similar to FIG. 1A. The unique point with FIG. 1B is the conventional TSOP 100b herein further includes second bonding wires 140b, and the lead frame 110 further includes bus bars 116, which are adjacent to the inner lead portions 112. In addition, the second bonding wires 140b are electrically connected between the bus bars 116 and the chip 120. However, the conventional TSOP 100b has the same problem as described.